Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless communication devices, personal digital assistants (PDAs), laptop computers, desktop computers, digital cameras, digital recording devices, cellular or satellite radio telephones, and the like. Digital video devices can provide significant improvements over conventional analog video systems in creating, modifying, transmitting, storing, recording and playing full motion video sequences.
A number of different video coding standards have been established for encoding and decoding digital video sequences. The Moving Picture Experts Group (MPEG), for example, has developed a number of coding standards including MPEG-1, MPEG-2 and MPEG-4. Other standards include the International Telecommunication Union (ITU) H.263 standard, QuickTime™ technology developed by Apple Computer of Cupertino Calif., Video for Windows™ and Windows™ media developed by Microsoft Corporation of Redmond, Wash., Indeo™ developed by Intel Corporation, RealVideo™ from RealNetworks, Inc. of Seattle, Wash., and Cinepak™ developed by SuperMac, Inc. Updated versions of these standards as well as new standards continue to emerge and evolve, including the ITU H.264 standard and a number of proprietary standards. Many image coding standards have also been developed for compression of still images, such as the JPEG standard. JPEG stands for “Joint Photographic Experts Group,” which is a standardization committee.
Some coding standards may make use of what is referred to as “AC/DC prediction.” AC/DC prediction is also sometimes referred to as “intra-prediction” and is generally the prediction process associated with intra-coding. For example, AC/DC prediction involves the prediction process of identifying another video block within a given video frame or image to be used in intra-coding to exploit redundancy within the given video frame or image to achieve data compression. In other words, intra-coding is generally an intra-frame or intra-image process of compressing the amount of data needed to code the video frame or image, and AC/DC prediction is the process of identifying which neighboring video block should be used to intra-code a current video block.
Intra-coding may be used alone as a compression technique, such as for still image compression, but is more commonly implemented along with other video coding techniques in the compression of video sequences. For example, intra-coding may be used in conjunction with inter-frame coding techniques that utilize similarities between successive video frames, referred to as temporal or inter-frame correlation. When intra-coding is used with inter-frame compression, video sequences can be compressed more than when inter-frame compression is used exclusively.
For intra-coding, the coder may utilize a mode-selection engine, which selects the desired mode for AC/DC prediction. Most video coding standards allow for at least two possible AC/DC prediction modes, including an AC prediction mode and a DC prediction mode. DC prediction refers to intra video block prediction that uses only the DC coefficient of video blocks (typically the upper left coefficient which may represent the zero frequency value of a video block or average value of a video block). AC prediction refers to intra video block prediction that uses some or all of the AC coefficients of a video block, which are the remaining (non-DC) coefficients of the video block.